Evolution Chapter 11

Slide 2 of 30  Do penguins reproduce asexually or sexually?  What does this tell us about these penguins?

Slide 3 of 30 Basketball Team Analogy  You want to put together a winning basketball team.  Do you want a large or small number of people to show up for tryouts?  Do you want students from one school or from multiple schools?  Do you care if the players have mothers or fathers, etc. who played basketball?  Do you care about the hair color of the players?

Slide 4 of 30 Guiding Questions  What is the nature of genetic variation in populations?  How do biologists measure variation in a population?

Slide 5 of 30 Population  Population – a group of members of the same species in the same area  Phenotype – a trait produced by one or more genes  In a population, there will likely be a range of phenotypes  Natural selection works on phenotypes, not genotypes  Example, even though some contract HIV, they have no symptoms  Penguins that are better swimmers will get food when it is in short supply

Slide 6 of 30 Population (Page 2)  Genetic variation is stored in a population’s gene pool  Gene pool – the combined alleles of all the individuals in a population  Allele Frequency – measure of how common an allele is in a population  A population consists of 5 individuals: 4 homozygous dominants (AA), 4 Heterozygotes (Aa), & 2 Homozygote Recessive (aa)  What is the frequency of the A allele?  What is the frequency of the a allele?

Slide 7 of 30 Question 11.1  1. What is the relationship between allele frequencies and a gene pool?  2. How did Mendel manipulate the gene pool of pea plants in his experiments?  What are the allele frequencies in P generation?  Assume equal numbers of both purebreeds  F1 generation?  F2 generation?

Slide 8 of 30 Sources of Genetic Variation?  1. Mutation  Random change in a gene  What are the two main type of mutations?  ONLY mutations in which types of cells are capable of being passed on?  More individuals = more mutations  More mutations = ____ genetic variation  More genetic variation = ______ population

Slide 9 of 30 Sources of Genetic Variation?  2. Recombination  Meiosis  There are 2 main sources of genetic variation, what are they?  Fertilization  When the egg is fertilized by the sperm, we get a brand new combination of chromosomes  In each pair of homologous chromosomes, 1 chromosome is from ____ and the other is from ____

Section 11.2

Slide 11 of 30 Populations, not individuals, Evolve  Populations are characterized by a wide range of phenotypes  Think of height, there are a few who are very tall and a few who are very short  But most are intermediate in height  What type of inheritance results in a range of phenotypes?  Normal curve (Bell Curve) – graph of the frequency of each of the phenotypes in a population

Slide 12 of 30

Slide 13 of 30

Slide 14 of 30 So which phenotype is best?  If there is no better phenotype, then the trait will approximate a normal curve  Most phenotypes are normally distributed anyway  However, environmental conditions can change and favor certain phenotypes  So natural selection will lead to evolution in a population  Evolution is a change in allele frequencies of a population

Slide 15 of 30 Natural Selection = 1 of 3 changes  Natural Selection can lead to microevolution  Microevolution – observable change in allele frequencies of a population over time  3 Patterns:  1. Directional Selection  2. Stabilizing Selection  3. Disruptive Selection

Slide 16 of Directional Selection  Favors ONLY 1 of the phenotypic extremes  An extreme phenotype becomes common

Slide 17 of Stabilizing Selection  Intermediate phenotypes are selected for  BOTH phenotypic extremes are selected against

Slide 18 of 30

Slide 19 of Disruptive Selection  BOTH extreme phenotypes are selected for  Intermediate phenotypes are selected against

Slide 20 of 30

Section 11.3

Slide 22 of 30 Other Mechanisms of Evolution  1. Gene flow  Immigration & Emigration  2. Gene Drift  Random changes in allele frequencies  3. Sexual Selection  Traits that are not naturally adaptive, but enable successful reproduction

Slide 23 of 30 Gene Flow  Movement of alleles from one gene pool or population to another  Movement of alleles INTO a gene pool = increased genetic variation  Movement of alleles OUT of a gene pool = decreased genetic variation

Slide 24 of 30

Slide 25 of 30 Genetic Drift  Flip a coin 6 times, how many times should be heads, but how many times are actually heads?  Requires small population size  Results in a loss of population genetic diversity  2 processes that shrink a population enough to produce gene drift  Bottleneck Effect  Founder Effect

Slide 26 of 30 Bottleneck Effect  A population bottleneck is an event that greatly reduces the population  The population bottleneck can result in genetic drift  A reduction in population size leads to a type of genetic drift called the Bottleneck Effect  In turn leads to a change in allele frequencies

Slide 27 of 30 Bottleneck Examples  1. Elephant seals were hunted down to 20 individuals  Population rebounded to 100,000 but little genetic variation  New population was essentially inbred  2. Natural disaster reduces a population size  Hurricane kills off most of the insects on an island, but the few who survive look radically different than those on the mainland. Over time the island population grows back, but looks entirely different than the mainland population

Slide 28 of 30 Founder Effect  A type of Genetic drift that occurs after a small number of individuals colonize a new area  Results in a loss of genetic variation

Slide 29 of 30 Sexual Selection  Sexual selection occurs when certain traits increase mating success  There are 2 types of sexual selection:  Intrasexual selection:  Competition among males  Intersexual selection:  Males display certain traits to females in courtship

Slide 30 of 30 Intrasexual SelectionIntersexual Selection